Introduce android-config.h to ensure build-time defines can be set

As per comment in android-config.h: 

When android is built for a specific device the build is
modified by BoardConfig.mk and possibly other mechanisms.
   eg
   device/samsung/i9305/BoardConfig.mk: 
       COMMON_GLOBAL_CFLAGS += -DCAMERA_WITH_CITYID_PARAM
   device/samsung/smdk4412-common/BoardCommonConfig.mk:
       COMMON_GLOBAL_CFLAGS += -DEXYNOS4_ENHANCEMENTS

This file allows those global configurations, which are not
otherwise defined in the build headers, to be available in
hybris builds.

Typically it is generated at hardware adaptation time.

Some reduction in support scripts too.